I was a bit concerned since it was loudest at the bottom of the engine, but I've heard any type of rod knocks don't get better after a few seconds of running.
Maybe I'll stick to a synthetic blend or conventional oil instead of the full syn. Sometimes engines that have been using conventional their whole life aren't happy with synthetic because of the different flow properties. I have heard many times people would say with synthetic on a higher mileage engine, their lifters make more noise, and going back to conventional it stops. One guy even went as far as saying his engine didn't like mobil 1 synthetic, but was fine with another brand of full syn.